Klystron tuning structure



NOY. 25, 1958 o, L LARKlN 2,862,138

v KLYSTRON TUNING STRUCTURE Filed Nov. 15,',1956 2 sheets-sheet 1 E|OR ART I2 l2 INVENTOR.

OSCAR L.. L AlZKIN ATTOIZ N E Y Nov. 25, 1958 o. L. LARKIN KLYsTRoN TUNING STRUCTURE 2 Sheets-Sheet 2 Filed Nov. 13, 1956 INVENTOR. @SGAE L., LAEZKI M "gm if ATTORNEY nited States Patent 2,862,138 Patented Nov. 25, 1958 KLYSTRON TUNING vSTRUCTURE Oscar L. Larkin, Allston, Mass., 'assignor to vBomac Laboratories Inc., Beverly, `Mass.,a corporation of Massachnsetts Application November 13, 1956, Serial No. 621,530

1 Claim. (Cl. S15-5.53)

`such tubes comprise two spaced anges joined to the tube sections which are operatively connected by a resonant cavity. A flexible diaphragm defines one end of this cavity and various tuningstructures have heretofore been disclosed in the prior art to alter the ange spacings. Included in such prior art structures are spring-loaded or lever-actuated mechanisms. These tuning structures have proven to be unsatisfactory either because of cumbersome `components extending beyond the overall tube envelope or because of spring resonances under conditions of severe shock and vibration.

In other structures a bolt and jam nut arrangement is provided to vary the distance between the flanges. However, it has been noted that once the desired frequency has been attained by rotation of the bolt, subsequent tightening to lock the nut will result in de-tuning of this frequency. Another disadvantage exists in that unskilled operators may seriously damage the tube grid structure by jamming or cause an electrical short circuit by contacting of the grids.

The present invention has for its primary object, therefore, the provision of an improved tuning structure for klystron tubes.

A further object is to provide a klystron tuning structure which is capable of withstanding severe shock and vibration.

A still further object is to provide a klystron tuning structure which incorporates certain safety features to eliminate damaging `of critical tube components.

Other objects, features and advantages will be evident after consideration of the following detailed description and reference to the accompanying drawings, in which:

Fig. l is a perspective view of a prior art embodiment;

Fig. 2 is a perspective view of the illustrative embodiment ofthe invention;

Fig. 3 is an enlarged detailed cross-sectional view of the illustrative embodiment; and

Figs. 4, 5 and 6 show a novel locking arrangement for the illustrative embodiment.

Referring now to Fig. 1 there is shown a klystron tube 1 of the so-called reflex type wherein the cavity body block 2 supports the reflector assembly 3 and houses the internal grid structure which is shown in greater detail in Fig. 3. A plurality of grids are disposed in the electron beam from the cathode supported within member 5. The resonator grid 27 is positioned within resonant cavity 28 formed in body block 2 and grid 29 is disposed adjacent the retiector 30. Grid 27 is variable with respect to grid 29 by means of movement of flexible diaphragm 7 which forms an end wall of cavity 28.

Tuning bracket 4 is secured to cathode support mem- -ber 5 with the inner conical member 6 joined to diaphragm 7. Slotted bolts 8 and 9 together with nuts 10 disposed-on either side of bracket 4 and nuts 11 bearing against body 2 provide means for adjustment of the resonant cavity diaphragm 7 to tune the tube. Suitable electrical conductors 12 for the cathode and reflector electrodes are provided and terminate in a pronged connector (not shown).

In accordance with the prior art method of adjustment of the spacing between bracket 4 and body 2, the nuts 11 are first brought up tightly to bear against the underside -of cavity body block 2. Next the spacings are adjusted so that the tube tunes to the mid-band :of the frequency range. Nuts 10 are then tightened against bracket 4 and conductors 12 are positioned as shown in Fig. 1.

It will be obvious that subsequent tuning adjustments may be made only on the bolt 8 side since wrenches must be employed. By loosening of the upper nut 10 and tightening of the bottom nut or vice versa such tuning is accomplished. In practice, however, it has been observed that even after the desired frequency is attained the subsequent tightening to prevent further movement results in detuning ofthis frequency. Hence, numerous adjustments and readjustments are necessary with accompanying delays. Further, no suitable protection is provided to assure that the operator will not damage the grid structure or cause a short circuiting of the grid elements by bringing'the elements in too close.

In accordance with the teachings of the present invention, as shown in Figs. 2 and 3, I have eliminated the prior art diiculties and provided fail-safe protection against grid jamming or damage.

A bolt 13 threaded into cavity body block 2 and bracket 4 is secured at its ends by nuts 14 and 15 with an intermediate nut 16 bearing against bracket 4. Caps 17 may then be secured to enclose nuts 14 and 15 to prevent any further manipulation. During assembly a differential screw 18 is inserted into cavity body block 2 until shoulder 19 contacts the underside of said block. Bracket bolt 20 is then threaded on nut 21 and into the internal thread of diierential screw 18. The bracket bolt 20 is then adjusted until the klystron oscillates at the upper frequency limit. Nut 21 is then tightened against bracket 4 to lock it in this position. Subsequent unwinding of screw 18 by means of a tool inserted in slot 26 will then bring bracket 4 closer to body 2 to thereby tune to the lower frequency limit. The travel of the bracket towards the body block 2 will terminate when the bottom surface of nut 21 bears against surface 22. This feature prevents tube damage and removal of screw 18 by an unskilled operator.

It may be noted that bracket bolt 20 is provided with an upper portion 23 of larger cross-section with an unthreaded portion 24 and lower threaded portion 25 of narrower cross-section to engage the internal threads of screw 18. According to the principal feature of the present invention, the selection of the thread combinations in the pitch of the outside thread of screw 18 indicated as A, as compared to the pitch of the portion 25 of bolt 20 indicated as B is important. In order to have the vertical displacement of the bracket follow in the same direction as the differential tuner screw 18 the pitch A must be greater than that of pitch B. To state this prerequisite numerically, we may assume that the pitch of A is .004 or 25 T. P. I. and the pitch of B is .0025" or 40 T. P. I., the net axial movement will then be .0015 for each revolution of diiferential screw 18. Selection of a good thread class fit such as a class 3 or 4 is preferred to provide for positive engagement of bolt 20 in screw 18 with a minimum of play. After the preliminary factory settinghas been made the head of bolt 20 may be enclosed with cap 17. Tuning of the device will ,may be substituted at the end of screw 18 and in this manner various predetermined settings could be provided to accurately determine the appropriate frequency.

In high shock and vibration conditions, a novel locking feature may be incorporated in the embodiment to retain screw 18 in its desired tuned position without fear of displacement by severe vibration or impact found in such applications as guided missiles. Referring now to Fig. 4 there is shown an exploded view of the components illustrated in Fig. 3 and a coiled member 31 adapted to engage the external threads of the differential' screw 18 within body 2.v Member 31 may be selected from the so-called Heli-Coil screw lock inserts which are available commercially and comprise a plurality `of circular coils 32 of a resilient stainless steel wire with one or more grip coils 33 near the center. The grip coils approximate a hexagon or polygon in shape as shown in Fig. 5 which is a view along the line A-A in Fig. 4. As the differential screw 18 is run through the member 31, the grip coils 33 are forced to conform to the thread circle. This results in a very strong spring-like pressure on the bolt thread which gives a locking eiect. The locked screw may be rotated by applying a breakaway torque approximately the same as the assembly torque. The final assembly is shown enlarged in Fig. 6 to illustrate the gripping action of member 31 on screw 18 to rmly position same within body 2.

There is thus disclosed an improved tuning structure which eliminates many of the prior art disadvantages and also prevents tube failure due to the positive engagement of the critical movable components.

What is claimed is:

Tuning apparatus for a velocity modulated klystron tube having a body member defining a resonant cavity with grid electrodes mounted in opposed end walls thereof, one of said electrodes being movable to thereby permit altering the resonant frequency of said device and a metallic bracket member extending parallel to said body member connected to said movable grid electrode, said tuning apparatus comprising threaded members positioned within said body member and interconnecting said bracket and body members, one of said threaded members comprising a differential screw member threadably mounted in said body, said screw member defining an internal threaded passageway, a bolt member having an upper threaded portion and a lower threaded portion of narrower cross-section adapted to engage the internal threaded passageway, the pitch of the outer thread of said differential screw member being always greater than the pitch of the internal passageway thread to thereby eiect positive vertical displacement of said bracket member in a similar direction as movement of the differential screw in and out said body member and a coil member disposed between the outer thread of said differential screw and the body member, said coil member having an intermediate gripping structure of polygonal shape to retain said screw member in its desired position under conditions of shock and vibration.

References Cited in the file of this patent UNITED STATES PATENTS 2,425,738 Hansen Aug. 19, 1947 2,431,103 Bradley et al. Nov. 18, 1947 2,443,535 Haas June 15, 1948 2,466,058 Sorg Apr. 5, 1949 2,777,968 Kenyon Jan. 15, 1957 

